What is liberalism? The reduction of all values to the radically autonomous self and the equality of all such selves, and thus the emptying from life of every substantive good that is larger than or outside of the autonomous self. But the problem is, once all larger substantive goods have been gotten rid of, and the only thing left is the autonomous self and its free choices, what goods are left for the freely choosing autonomous self to choose?
Auster posed the question to explain why two American girls would be attracted to a sex and death music subculture, leading to their own murder. He observes that sex and death are two significant aspects of existence left to the liberal autonomous self.
The other side to the answer, though, is that once you get rid of the larger substantive goods you are left with the trivial ones. The autonomous self can encompass smaller goods such as entertainments, dining experiences, consumer choices, socialising and so on - so this is what the modern West excels at.